Heavy Steering

[124 ac]

Hi,

my V6 Emblema has very stiff and heavy steering. Has been for a while like that but last summer Servotronic worked normally a short time and car was very nice to drive..
I already cleaned the magvalve contacts in the steering unit but it did not helped, but Servotronic fault came so I think electronics are ok.
I assume I must remove magvalve from the servounit and maybe it is dirty and clocked but is there possibility to find new one or is it easier to buy whole steering unit from ebay.. ?
I have changed oil in system but I think oil will come of in this procedure so I have totally new oils after that, which is good also.

Anyone familiar with this problem, Servotronic is very common so there is probably same units also in other marks. I remember that eper has no number for that part..